1. Field of the Invention
This invention relates to a commercially advantageous method for the production of inorganic oxide particles prevented from agglomerating into coarse lumps and allowed to acquire a freely controlled diameter. These particles are commercially valuable as a carrier for chromatography, as a raw material for catalysts, and as a filler for pigments, solid lubricants, and coating materials and for synthetic resins used in manufacture of fibers and films, for example.
2. Description of the Prior Art
In the methods heretofore adopted for the production of inorganic oxide particles, the method which comprises spraying a metal oxide sol in a compressed state into a heated nonpolar solvent thereby converting the sol into a gel, the method which comprises spray drying a metal salt solution and calcining, the method which comprises emulsifying a metal salt solution and consequently effecting interfacial polymerization of the metal salt, and the method which comprises subjecting a metal alkoxide to hydrolysis or pyrolysis in an organic solvent or in a gaseous phase have been renowned. Among other conventional methods, the socalled wet methods which produce particles by subjecting a raw material compound to hydrolysis or neutralization in a solution has found widespread acceptance because these methods easily permit control of the diameter of particles to be produced and prevention of produced particles from agglomeration into coarse lumps. In these wet methods, those of the class based on the hydrolysis of a metal alkoxide in an organic solvent have been attracting special attention because of their ability to produce particles having a narrow particle size distribution and excelling in dispersibility. The methods of this class include the method which obtains amorphous silica particles from tetraalkoxy silane as a raw material [W. Stober et al, "J. Colloid and Interface Science", 26, 62-69 (1968), etc.], the method which obtains hydrated titanium dioxide particles from tetraethoxy titanium as a raw material [Barringer et al, "Langmuir," 1, 414 (1985), etc.], and the method which obtains hydrated aluminum oxide particles from tri-secbutoxy aluminum as a raw material [D. L. Catone at al, "J. Colloid and Interface Science," 48, 291 (1974), etc.], for example.
From these articles of literature, basic reaction conditions for obtaining spherical discrete particles by the hydrolysis of an alkoxy metal compound in an organic solvent such as alcohol can be inferred. When the kind of an alkoxy metal compound as a raw material is fixed, however, the diameter of produced particles cannot be freely varied from a certain limit even by changing the kinds of organic solvent and catalyst, the composition of raw material, and the reaction conditions such as reaction temperature. Especially when a tetraalkoxy silane is adopted as a raw material and a monohydric alcohol as an organic solvent, though the diameter of produced silica particles increases in proportion as the number of carbon atoms of the monohydric alcohol increases, the maximum diameter attainable at all is limited to 2 .mu.m. An attempt at heightening the concentration of produced particles or enlarging the diameter of produced particles by increasing the concentration of tetraalkoxy silane as a raw material with a view to commercial productivity has entailed a disadvantage that the produced particles have a widened particle size distribution and are liable to agglomerate into coarse lumps.
For the solution of this problem, Japanese Patent Laid-Open SHO 62(1987)-72,514 has disclosed a method for the production of silica particles which comprises hydrolyzing a tetraalkoxy silane in a water-containing alcohol solution thereby producing a slurry containing minute silica particles as seed particles and then continuing the supply of the alkoxy silane to the slurry thereby inducing growth of the seed particles. Though this method allows an addition to the diameter of produced particles, it cannot constitute an economic process for the production of discrete silica particles because an increase in the concentration of raw material for the purpose of enhancing the productivity only aggravates the occurrence of coarse lumps by agglomeration. Japanese Patent Laid-Open SHO 62(1987)-72,516 has disclosed a method which causes the existence of an alkali metal ion in a system having an alkoxy silane compound as a raw material sequentially supplied into an alcohol (monohydric alcohol) solution thereby effecting sequential growth of the diameter of particles being consequently formed therein. This method, however, is prone to a disadvantage that the produced silica particles suffer from inclusion of the alkali metal and the reaction calls for a long time and betrays inferior productivity.
An object of this invention, therefore, is to provide a novel method for the production of inorganic oxide particles.
Another object of this invention is to provide an economically advantageous method for the production of inorganic oxide particles of a desired diameter in a high concentration without entailing agglomeration of the produced particles into coarse lumps.